Pushbutton locks are well known and find many uses. A conventional combination lock can be used, for example, on a lockbox which stores an item such as a key. To gain access to the inside of the lockbox and the key, a correct combination must be selected from the outside of the lock and an open handle (i.e., knob) is rotated to retract a locking bolt and gain access to the inside of the lock. Conventional combination locks are discussed in the following U.S. patents, each of which is incorporated herein by reference in its entirety: 4,936,894; 5,768,921; 6,145,355; and 6,272,889.
Conventional locks can include an array of elongated buttons, each of which has, on the sides thereof, plural cut-outs, or “gates.” A case contains the lock and defines plural bores within which the buttons travel. The buttons are urged out of a front cover of the case toward the user by biasing springs. Plural latching members cooperate with features on the button array to hold same in a depressed position against the force of the biasing springs when the buttons are pushed in by an operator of the lock.
The conventional lock further includes a locking bolt which is coupled to a checker plate. The checker plate defines plural edges that engage the sides of the button assemblies and are received in the gates therein if the buttons are properly positioned. The checker plate is slidably mounted in a track within the case and is normally urged to a first end of the track by another biasing spring. When the checker is at this first end of its travel, the bolt is in its locked position.
The knob is coupled to the checker plate and can be operated to urge the checker plate towards a second end of its track. However, the checker plate is prevented from moving to the second end of its track if the portions of the buttons engaged by the edges of the checker plate do not include gates.
By the foregoing arrangement, all of the buttons must be properly positioned, either in or out, if the checker plate is to be moved to its second position so as to move the bolt to the unlocked position. If even one button is incorrectly positioned the checker plate will contact the button assembly at a location which does not include a gate, which prevents the checker plate from moving to its unlocked position.